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Mechanism of Action
AGGRASTAT is a reversible antagonist of fibrinogen binding to the GP IIb/IIIa receptor, the major platelet surface receptor involved in platelet aggregation. When administered intravenously, AGGRASTAT inhibits ex vivo platelet aggregation in a dose- and concentration-dependent manner.
When given according to the PRISM-PLUS regimen of 0.4 mcg/kg/min over 30 minutes followed by a 0.1 mcg/kg/min maintenance infusion, > 90% inhibition of platelet aggregation is attained by the end of the 30-minute infusion. When given according to the recommended regimen of 25 mcg/kg over 3 min followed by a 0.15 mcg/kg/min maintenance infusion, > 90% inhibition of platelet aggregation is attained within 10 minutes. Platelet aggregation inhibition is reversible following cessation of the infusion of AGGRASTAT.
AGGRASTAT inhibits platelet function, as demonstrated by its ability to inhibit ex vivo adenosine phosphate (ADP)-induced platelet aggregation and prolong bleeding time in healthy subjects and patients with coronary artery disease. The time course of inhibition parallels the plasma concentration profile of the drug.
Following discontinuation of an infusion of AGGRASTAT 0.10 mcg/kg/min, ex vivo platelet aggregation returns to near baseline in 4 to 8 hours in approximately 90% of patients with coronary artery disease. The addition of heparin to this regimen does not significantly alter the percentage of subjects with > 70% inhibition of platelet aggregation (IPA), but does increase the average bleeding time, as well as the number of patients with bleeding times prolonged to > 30 minutes. Similar platelet aggregation recovery rates are observed following discontinuation of a 0.15 mcg/kg/min infusion.
Tirofiban has a half-life of approximately 2 hours. It is cleared from the plasma largely by renal excretion, with about 65% of an administered dose appearing in urine and about 25% in feces, both largely as unchanged tirofiban. Metabolism appears to be limited.
Tirofiban is not highly bound to plasma proteins and protein binding is concentration independent over the range of 0.01 to 25 mcg/mL. The unbound fraction in human plasma is 35%. The steady state volume of distribution of tirofiban ranges from 22 to 42 liters.
In healthy subjects, the plasma clearance of tirofiban ranges from 213 to 314 mL/min. Renal clearance accounts for 39 to 69% of plasma clearance.
There is no effect on clearance of tirofiban by sex, race, age, or hepatic impairment.
Plasma clearance of tirofiban is decreased about 40% in subjects with creatinine clearance < 60 mL/min and > 50% in patients with creatinine clearance < 30 mL/min, including patients requiring hemodialysis [see DOSAGE AND ADMINISTRATION]. Tirofiban is removed by hemodialysis.
Two large-scale clinical studies established the efficacy of AGGRASTAT in the treatment of patients with NSTE-ACS (unstable angina/non-ST elevation MI). The two studies examined AGGRASTAT alone and added to heparin, prior to and after percutaneous coronary revascularization (if indicated) (PRISM-PLUS) and in comparison to heparin in a similar population (PRISM). These trials are discussed in detail below.
PRISM-PLUS (Platelet Receptor Inhibition for Ischemic Syndrome Management — Patients Limited by Unstable Signs and Symptoms)
In the double-blind PRISM-PLUS trial, 1570 patients with documented NSTE-ACS within 12 hours of entry into the study were randomized to AGGRASTAT (30 minute initial infusion of 0.4 mcg/kg/min followed by a maintenance infusion of 0.10 mcg/kg /min) in combination with heparin (bolus of 5,000 U followed by an infusion of 1,000 U/h titrated to maintain an APTT of approximately 2 times control) or to heparin alone. All patients received concomitant aspirin unless contraindicated. Patients who were medically managed or who underwent revascularization procedures were studied. Patients underwent 48 hours of medical stabilization on study drug therapy, and they were to undergo angiography before 96 hours (and, if indicated, angioplasty/atherectomy, while continuing on AGGRASTAT and heparin for 12-24 hours after the procedure). AGGRASTAT and heparin could be continued for up to 108 hours. Exclusions included contraindications to anticoagulation, decompensated heart failure, platelet count < 150,000/mm³, and serum creatinine > 2.5 mg/dL. The mean age of the population was 63 years; 32% of patients were female and approximately half of the population presented with non-ST elevation myocardial infarction. On average, patients received AGGRASTAT for 71 hours.
A third group of patients was initially randomized to AGGRASTAT alone (no heparin). This arm was stopped when the group was found, at an interim look, to have greater mortality than the other two groups.
The primary endpoint of the study was a composite of refractory ischemia, new MI and death within 7 days. There was a 32% risk reduction in the overall composite primary endpoint. The components of the composite were examined separately and the results are shown in Table 5. Note that the sum of the individual components may be greater than the composite (if a patient experiences multiple component events only one event counts towards the composite).
Table 5 : Primary outcomes at 7 days in PRISM-PLUS
|Endpoint||AGGRASTAT + Heparin
|Death, new MI, and refractory ischemia at 7 days||12.9%||17.9%||32%||0.004|
The benefit seen at 7 days was maintained over time. The risk reduction in the composite endpoint at 30 days and 6 months is shown in the Kaplan-Meier curve below.
Figure 1: Time to first event of death, new MI, or
refractory ischemia in PRISM-PLUS
An analysis of the results by sex suggests that women who are medically managed or who undergo subsequent PTCA/atherectomy may receive less benefit from AGGRASTAT (95% confidence limits for relative risk of 0.61-1.74) than do men (0.43-0.89) (p=0.11). This difference may be a true treatment difference, the effect of other differences in these subgroups, or a chance occurrence.
Approximately 90% of patients in the PRISM-PLUS study underwent coronary angiography and 30% underwent angioplasty/atherectomy during the first 30 days of the study. The majority of these patients continued on study drug throughout these procedures. AGGRASTAT was continued for 12-24 hours (average 15 hours) after angioplasty/atherectomy. The effects of AGGRASTAT at Day 30 did not appear to differ among sub-populations that did or did not receive PTCA or CABG, both prior to and after the procedure.
PRISM (Platelet Receptor Inhibition for Ischemic Syndrome Management)
In the PRISM study, a randomized, parallel, double-blind study, 3232 patients with NSTE-ACS intended to be managed without coronary intervention were randomized to AGGRASTAT (initial dose of 0.6 mcg/kg/min for 30 minutes followed by 0.15 mcg/kg/min for 47.5 hours) or heparin (5000-unit intravenous bolus followed by an infusion of 1000 U/h for 48 hours). The mean age of the population was 62 years; 32% of the population was female and 25% had non-ST elevation MI on presentation. Thirty percent had no ECG evidence of cardiac ischemia. Exclusion criteria were similar to PRISM-PLUS. The primary endpoint was the composite endpoint of refractory ischemia, MI or death at the end of the 48-hour drug infusion. The results are shown in Table 6.
Table 6 : Primary outcomes in PRISM – Cardiac Ischemia
|Composite Endpoint (death, MI, or refractory ischemia)||AGGRASTAT
|2 Days (end of drug infusion)||3.8%||5.6%||33%||0.015|
In the PRISM study, no adverse effect of AGGRASTAT on mortality at either 7 or 30 days was detected. This result is different from that in the PRISM-PLUS study, where the arm that included AGGRASTAT without heparin (n=345) was dropped at an interim analysis by the Data Safety Monitoring Committee for increased mortality at 7 days.
Last reviewed on RxList: 11/6/2013
This monograph has been modified to include the generic and brand name in many instances.
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